Effect of Corynebacterium parvum on the course of a Listeria monocytogenes infection in normal and congenitally athymic (nude) mice.

Spleen counts of Listeria monocytogenes in normal mice challenged with various numbers of organisms were generally lower in mice injected 3 days previously with killed Corynebacterium parvum. This increased resistance was unexpected since C. parvum generally inhibits T cell-mediated immunity, the functional immunity against Listeria being T cell-dependent. The inhibitory effect on T cells seemed to be compensated by the stimulatory effect of C. parvum on macrophages. Therefore, the experiments were repeated in congenitally athymic (nude) mice (B10LP) lacking functional T cells. C. parvum pretreatment of nu/nu mice prolonged the time between challenge and death, the number of survivors in the pretreated and non-treated mice being approximately equal. It was concluded that C. parvum exerted a stimulatory effect on macrophages resulting in a higher resistance against Listeria.